1. Field of the Invention
The present invention relates to an auxiliary power source device for the motor driven camera in which the motor driven device is built or on which it is mounted in order to increase the film winding speed.
2. Description of the Prior Art
Quite recently various kinds of motor driven cameras for carrying out the film winding and the shutter charge by means of a motor have been brought into practice, whereby the motor drive device is attached on the camera body or the motor is built in the camera body. As the power source for these motor driven camera the dry battery or the secondary battery is used, whereby it is mostly built in or fixed in the motor drive device. Consequently, the size and the weight of the power source is desired to be as compact and light as possible. Especially, in case of the camera in which the winding motor is built or the automatic winder it is desired to realize the circuit and the construction in such a manner that as small number of as compact batteries as possible are used, in order to obtain a small and light device. However, when the number of the batteries is decreased the winding speed and the shooting capacity are also decreased.
Generally the characteristics of the winding DC motor for the motor driven camera is shown with the curves A (output torque-consumed current characteristics) and B (output torque-speed characteristics) in FIGS. 1(a) and (b) respectively. The characteristics can be represented as follows: EQU I=C.sub.1 .pi.+C.sub.2 ( 1) EQU N=C.sub.3 V-C.sub.4 .tau. (2)
Hereby, I: consumed current, .tau.: rotation torque, V: power source voltage, C.sub.1 -C.sub.4 : constant, and N: speed.
When such a motor is used as the winding motor for the motor driven camera, it is desired to choose the constant C.sub.3 in (2) large (namely, the diameter of the wire of the motor coil large) and the speed of the motor large in order to drive the motor with high efficiency and high output. However, it is impossible to increase the speed of the motor so highly due to the construction of the bearing and so on, whereby ordinarily the no-load speed (namely .tau.=0) is 10,000-15,000 r.p.m.
There is little problem when the above-mentioned motor is used for the ordinary photographing (for example snap picture) even if the winding speed is low or the shooting capacity is small, while it becomes necessary to increase the winding speed or the shooting capacity in order to carry out the continuous photographing such as for sports photography.
As the solution for the above, for example, the U.S. Pat. No. 3,853,396 discloses a method in accordance to which the auxiliary power source is connected in series to the driving power source. However, if the auxiliary power source is only connected in series to the driving power source, as is clear from (2) only V becomes large and the curve B in FIGS. 1(a) and (b) is translated parallely so that the curve when the auxiliary power source is used becomes D (output torque-speed characteristics). Then, as is clear from FIG. 1(a) and formula (2), the starting torque (when the speed is 0) is increased from .tau..sub.1 up to .tau..sub.2, while as is clear from FIG. 1(a) and formula (1), the starting current is increased from I.sub.1 up to I.sub.2. Thus, in case of the conventional device the starting torque is increased so that when the auxiliary power source is used a too high torque is applied to the film when a predetermined number of pictures have been taken with the result that the film is often damaged, which is inconvenient. Further, the starting current is also increased so that the motor control switch, the transistors and so on for large current have to be used in the motor driven camera with the result that the manufacturing cost of the motor driven camera increases while its size becomes also large.
Further, not only the starting torque and the starting current are increased but also, as is clear from FIG. 1(b), the no-load speed N.sub.2 is also increased so that, as mentioned above, the no-load speed ranging from 10,000-15,000 r.p.m. which is achieved by the driving power source alone is increased further when the auxiliary power source is used, and this shortens the life of the motor and often damages it, which is inconvenient. Further, in order to eliminate the above shortcomings, a motor with governer has been proposed, whereby the motor is complicated in the construction so that the manufacturing cost is high and there easily takes place damage, which is inconvenient.